Personally I think the 5 looks good, and I thought the 4/4S looked good too. I will be getting a 5, I currently have a 3GS, and before that I had 2 RAZRs (flip phones not smartphones) and before that a Motorola StarTAC. That thing was made out of plastic, but it was nice, durable plastic that felt "premium" somehow. The RAZRs were metal, of course, and that was one of the things that I loved about those phones.
I have gone case-less with my 3GS, and it's looking kinda crappy now, although the glass has never cracked it has a few scratches, and the plastic on the sides and back is in bad shape (1 small crack near the Dock connector). I am looking forward to getting a 5, and I think that the extreme slimness will make me more likely to put some kind of protective case over it. With a reasonably protective yet still minimal case (e.g. Magpul) it will still probably be dimensionally comparable to many Android phones.